The Environmental Protection Agency is working aggressively to reduce pollution in automobiles and heavy-duty diesel trucks and buses. One device used to reduce pollutants is as a catalytic converter. Catalytic converters reduce pollution by enhancing the conversion rate of pollutants, such as nitrous oxides (“NOx”), into harmless gases, such as nitrogen and water vapor. One type of device that uses a catalytic converter is a selective catalytic reduction (“SCR”) muffler.
One example of a SCR muffler is disclosed in U.S. Patent Application Publication Number 2008/0216470 to Sedlacek et al. (“the '470 Publication”). The '470 Publication discloses an exhaust aftertreatment system. Exhaust flows from an engine to an aftertreatment system, such as a SCR muffler. The exhaust is pre-treated with urea before entering the aftertreatment system. The aftertreatment system includes a straight pipe inlet disposed laterally across a chamber. The exhaust gas flows laterally into the straight pipe inlet and out axially through perforations in the pipe wall. The exhaust gas then passes over a catalytic substrate that converts some of the exhaust gases (e.g., NOx) into harmless gases.
A problem with the system disclosed in the '470 patent is that urea does not adequately convert into ammonia and ammonia does not adequately mix with the exhaust gas, which leads to an unoptimized gas mixture and a non-uniform gas distribution across the surface of the catalyst. An unoptimized gas mixture and non-uniform gas distribution reduces the effectiveness of the catalytic reactions, allowing an increased concentration of pollutants (e.g., NOx) to escape to the atmosphere. Therefore, what is needed is an exhaust treatment system that can provide a more optimized gas mixture and distribution across the surface of a catalyst.